Reed switch

ABSTRACT

A plunger is slidably mounted in a housing so as to move along a predetermined path. A pair of laterally spaced apart magnets is operatively engaged by the plunger so as to be movable parallel to the predetermined path. A pair of magnetically-responsive contacts is disposed between the paths of the magnets, which contacts are switched from one condition to the other in response to movement of the magnets in one direction and is then switched back to the original condition by movement of the magnets in the other direction.

United States Patent [1 1 Straub Aug. 14, 1973 REED SWITCH Primary Examiner-Roy N. Envall, Jr. tn C d, N b [75] Inventor Emil R C S ub, oza e r Attorney-Dav! A. vogel [73] Assignee: Vectronix, lnc., Cozad, Nebr. 22 Filed: May 18, 1972 [571 ABSTRACT A plunger is slidably mounted in a housing so as to [21] Appl' 254'724 move along a predetermined path. A pair of laterally spaced apart magnets is operatively engaged by the [52] Us. Cl. 335/207, 335/206 p ng so as to be movable par llel to the predeter- [51] Int. Cl. H01h 13/14 n d p h- A pair of magnetically-responsive contacts [58] Field of Search 335/205, 206, 207 is disposed between the paths of the gn h h contacts are switched from one condition to the other [56] Refe m Cit d in response to movement of the magnets in one direc- UNITED STATES PATENTS tion and is then switched back to the original condition 3,488,613 1/1970 Marchetti 335/207 by movement the magnets m the 3,243,544 3/1966 Mayer 335/207 X 21 Claims, 5 Drawing Figures Patented Aug. 14,1973 3,753,179

3 Shets-Sheet l I a: FlGl eo IO Patented Aug. 14, 1973 3 Sheets-Sheet I5 FIG. 3

FIG.

FIG. 5

I I l I I 1 r 1 .ll

REED SWITCH This invention is directed to a switch utilizing magnetically-responsive contacts which are actuated by a magnetic field.

An object of this invention is to provide a push.- button. reed. switch which is switched from one condition to another by depressing the button, and which is switched back to the original condition when the but.- ton is released, such that the distance between the switching points is reduced.

A further object is to provide a reed switch having two pairs of contacts respectively operated by associated pairs of magnets, wherein the effect ofone pair of magnets on the opposite pair of contacts isxminimized.

A still further object is to provide a reed switch usable in conjunctionwitha number of other similar reed switches on a keyboard, wherein the magnets inone switch have a minimum effect on the contacts in other switches.

A yet further object is to provide a reed switch which has space for a l'amp therein.

Further objects, advantages, and details of the invention will=be apparentasthe. descriptionproceeds, reference being had to the accompanying drawingswherein preferredforms of'the invention are shown. It will" be understood, however, that the description and drawings are illustrative only, and that the scope of the in vention is to be. measured by the appended claims.

F 1G. 1 is a view in longitudinal crosssection of a reed switch. incorporatingthe features of the present invention;

FIG. 2' is a view inlongitudinal cross section taken along the. line 2'-2.of FIG. 1,.without the leads to the reed switching. elements being shown;

FIG. 3 isaview in transverse crosssectionof the reed'.

switchof FIGS. 1: taken along the line 3*-3 thereof;

FIG. 4 isa view in longitudinal cross section of the reed switch of FIG. 1 taken along the'line 44 thereof;

keyboard ll,.the keyboa-rd. l'l'. havinga hole l2 to accommodate a projection on the reedswitch as will:

be described. A- threaded bolt' 13 is provided which passes throughanopening in the keyboard 11 for threaded'engagement with the-reed switchlo so asto hold samein a selected'location.

The reed switch 10 comprises ahousing which' is rectangular in transverse. cross section and, in the form shown, is constructed'of plastic. The housingi20 'has an abutmentv or. wall. 21 adjacent to one end thereof, a.

neck 22 beingiprovided on the wall 21 and'protruding outwardly. therefrom. An. opening 23 extends through the wall2 l and the neck 22, with the opposite end of the housing 20 being open. The housing 20 is definedbya setof four sidewalls 24. There is prov-ided'a pair oflaterally aligned and longitudinally extending guides or rails 25 (FIG. 3) on two of the walls 24, which rails 25 extend generally parallel to each other in the longitudinal direction of the housing 20. There is also provided a base having a rectangular bottom wall 31 and four side walls 32, which side walls fit into and frictionally engage respectively the inside of the side walls 24 of the housing 20. Formed on the bottom wall 31 and protruding outwardly therefrom is a projection 33 which fits into the hole 12 formed in the keyboard 11, thereby to prevent turning of the reed switch 10 as it is secured to the board 11 by means of the bolt 13. Protruding inwardlyin the same direction as the side walls 32. is a cylindrical lug 34. After'the parts are properly located within the housing 20, the base 30 is force fitted into theopen end of the housing 20. In addition to the frictional engagement, it is preferable to use cement to insure a long lasting connection.

There is also provided a hollow post 40 which is press fitted onto the lug 34 so as to project upwardly therefrom. In the upper end of the post 40 there are provided four holes 41', 42, 43, and 44 (FIG. 3 specifically) which are arranged in the form of a square. A pair of leads 45 passes through the post 40 into the holes 41 and 43, the other ends of the leads 45 passing through the base-30 and protruding therefrom. A U-shaped wire 46has the legs thereof located respectively in the holes 41 and 44; and another U-shaped wire 46 has its legs located respectively in the holes 42 and 43. The holes 42 and 44' thereforedefine a socket to receive the leads 47 of a lamp 48. The lamp 48 may be used in a number of ways, such as to indicate that the reed switch 10- should be actuated, or the lamp 48 may be always on,

so that the operator can see the switch. Such lamp 48,.

however, is not. necessary to the instant invention.

Mounted on the base 30 and extending upwardly therefrom is a pair of reed switching elements 50 and 55. The switching element 50 consists of an elongated glass envelope 5 1 which is hermetically sealed and containsan inert gas. Encased' in the envelope 51 is a pair of beams 52 which arevery thin, narrow metal strips that are directed toward one another and extend in a direction substantially parallel to the longitudinal axis of the housing 20. Respectively at the ends of the beams 52" are contacts 53 which" are spaced from each other; that is, the contacts 53 are normally open. The

lower beam 52 is shorter than the'upper beam 52",

whereby the contacts are located near the lower end of the envelope 5]. The beams 52 respectively penetrate the ends of the envelope 51 and are connected to terminals 54 which pass through the base 30 and protrude-outwardly therefrom. When the contacts 53 are oppositely magnetically poled so as to be attracted to each other, they will close. This occurswhen they are exposed to amagnetic field'with sufficient magnitude to overcome the rigidityof the beams 52. The beams 52 are constructed to possess the characteristic of a leaf spring, so that,v when their mechanical stiffness-is overcome by the strength of magnetic attraction, the contacts 53 close.

The other switching element 55' consists of an elongated glass envelope 56 which is hermetically sealed andcontains an inert gas. Encased in the envelope 56 is a pair of beams 57'which-are in the form of very thin, narrow, metal strips that-are directed toward one another and extend in a direction substantially parallel to thelongitudinalaxisof the housing 20'. Respectively at the ends of'the beams$7 are'contacts 58 which contact each other; that is, the contacts 58 are normally closed.

The lower beam 57 is longer than the upper beam 57, whereby the contacts 58 are located near the upper end of the envelope 56. The beams 57 respectively penetrate the ends of the envelope 56 and are connected to terminals 59 which extend through the base 30 and protrude outwardly therefrom. When the contacts 58 are oppositely magnetically poled so as to be attracted to each other, they will close. This occurs when they are exposed to a magnetic field with sufficient magnitude to overcome the rigidity of the beams 57. The beams 57 are constructed to possess the characteristic of a leaf spring, so that, when their mechanical stiffness is overcome by the strength of the magnetic attraction, the contacts 58 close.

Actually, the switching elements 50 and 55 may be identical, with one being inverted with respect to the other. The switching elements 50 and 55 are mounted within the housing 20 adjacent opposite ones of the side walls 24, each being arranged generally centrally with respect to its associated side wall.

The reed switch further comprises a plunger 60 which includes a block-like body 61 having a central bore 62 extending therethrough, which bore 62 has an increased diameter portion 63 at its lower end. The juncture between the increased diameter portion 63 and the rest of the bore 62 defines a laterally-extending abutment surface 64. Formed respectively in the shorter sides of the body 61 are longitudinallyextending channels 65 and 66. Formed in the longer sides of the block-like body 61 are longitudinallyextending grooves 67. Formed in the corners of the body 61 on both sides of the channel 65 is a pair of laterally-spaced-apart, longitudinally-extending bores 68. Similarly, there is formed in the opposite comers of the body 61 on both sides of the channel 66 a pair of laterally-spaced-apart, longitudinally-extending bores 69. The body 61 finally has a laterally-extending surface 70 at its lower end.

The upper end of the body 61 defines a shoulder 71 and carries an upwardly-directed sleeve 72 having a diameter slightly less than the diameter of the opening 23 in the neck 22 of the housing 20. In the base of the sleeve at diametrically-opposed areas thereon are generally-rectangular openings 73. There is provided a pair of notches 74 at diametrically-opposite areas on the outer end of the sleeve 72. Y

The reed switch 10 further comprises two pairs of magnets 75 and 76, each of which is a solid cylinder and is axially magnetized so as to have north and south poles at opposite ends. The diameter of each magnet 75 is approximately equal to the diameter of the bores 68 and is frictionally engaged therein. Similarly each magnet 76 has a diameter approximately equal to the diameter of the bore 69 and is frictionally held therein. The length of each magnet 75 and 76 is approximately equal to the length of the respective bores 68 and 69, so that the outer end of each magnet is approximately flush with the surface 70 of the body 61.

The reed switch 10 also includes a spring 77 which encircles the post 40 and the lamp 48 thereon. One end of the spring 77 rests against the bottom wall 31 of the base 30, and the other end fits within the increased diameter bore portion 63 of the plunger 60 and rests against the abutment surface 64. The channel 65 is aligned with the switching element 50, and the channel 66 is aligned with the switching element 55. Thus, when the plunger 60 is depressed or moved toward the base 30, the switching elements 50 and 55 respectively ride in the channels 65 and 66. The neck 22 of the housing 20 slidably receives the sleeve 72 of the plunger 60. The spring 77 urges the plunger 60 away from the base 30 so that the shoulders 71 are resiliently urged against the wall 21 of the housing 20. Thus, the upper limit of the plunger 60 is achieved when the shoulder 71 is against the wall 21. The lower limit of the plunger 60 results from the surface of the plunger 60 engaging the top surfaces of the side walls 32 on the base 30.

Lastly, the reed switch comprises a cap 80 which has a top wall 81 with four depending, slightly inclined side walls 82. On the interior of the top wall 81 is a depending tube 83 having a diameter approximately equal to the inner diameter of the sleeve 72. A pair of slots 84 is formed in diametrically opposed sides of the tube 83, and a pair of projections 85 is formed in the tube 83 nearest the top 81.

In assembling the cap 80, the tube 83 is inserted in the sleeve 72 which is frictionally engaged thereby. The projections 85 are fitted into the notches 74 on the sleeve 72. The slots 84 in the tube 83 are respectively aligned with the openings 73, in the sleeve 72 to permit air flow in the area of the lamp 48 for cooling the same. The cap 80 in the form shown in translucent, so that light emanating from the lamp 48 is visible.

In use, the reed switch is mounted on a keyboard 11, as previously explained, with the sets of terminals 54 and 59 being electrically connected to their respective circuits. When it is desired to operate such circuits, the user depresses the cap 80 which moves the plunger 60 downwardly, that is, toward the base 30, which, in turn, carries the magnets and 76 downwardly against the action of the spring 77.

When the magnets 75 are at their at-rest position, they are sufficiently removed from the contacts 53 that they are open. When the magnets 76 are in their at-rest condition, they are in such close proximity to the contacts 58 that they are closed. Thus the contacts 53 are normally open and the contacts 58 are normally closed. When the cap is depressed, the magnets 75 ap proach the contacts 58. When the magnets 75 have traversed a predetermined distance, the magnetic field presented to the contacts 53 will be sufficient to cause them to close. When the plunger 60 is ,depressed slightly further, the magnets 76 will be sufficiently removed from the contacts 58 to cause them to close, while the contacts 53 are still maintained closed by the magnets 75. When the cap 80 is released, the magnets 75 and 76 approach their original position, and the contacts 58 first close, followed by opening of the con-' tacts 53.

An important advantage achieved by the instant invention is that the total mass'of the two magnets used to operate a reed-switching element is less than that required of a single magnet, without any deterioration in performance. For example, whereas a magnet previously used was a cylinder having a diameter of onefourth inch and a height of one-fourth inch, the instant invention requires two cylinders each having a diameter of one-eighth inch and a height of one-fourth inch. The mass of two such 26 inch diameter magnets is exactly one-half the mass of a /4 inch diameter magnet. Although it is not fully understood exactly why two magnets, each having one-fourth the total mass of a single magnet, will perform comparably to the single magnet, it is believed that because the magnets are on opposite sides of the contacts they reinforce each other to compensate for the lower mass. While the magnets reinforce each other with respect to the contacts disposed therebetweeri, neither magnet has any increased effect with respect to the other pair of contacts in each switch.

A further advantage of the construction described relatesto the use of the reed switch in a keyboard. Because the total mass of each pair of magnets used to operate the associated reed switching element is substantially less than the mass heretofore required, such pair of magnetshas a reduced effect on the contacts in other ones of the reed switches; It may be seen there-' fore that the improved construction of the reed switch reduces magnetic interaction among the reed switches on a keyboard.

Another advantage resides in the specific construc tion of the reed' switch 10. By constructing such switch to have the magnets located around the periphery of the plunger, the center of the plunger 60 and the housing 20m available for other uses. Specifically in this instance, the plunger 60 is cut out centrally thereof, so that a lamp and associated socket may be provided.

One'further advantage appears to be an improvement in whatmay be'referred to as the switching differential. When the reed switch is actuated by depressing the cap 80, the plunger 60 and the magnets'75 and 76 carried thereby must reach a certain point before the contacts switch from one condition to the other. When the cap" 80is released, and the plunger 60 and the magnets 75 and 76 carried thereby return toward theirat-rest position, the contacts will'revert to their original position at a different point. The distance between these two points may be referred to as the switching differential. It has been found that the switching differential has been desirably reduced from that which occurred when a single magnet was used'to actuate the reed switching element.

Turning now to FIG. 5, an alternative embodiment of the present invention is illustrated. Specifically, the plunger 60 includes two bores 68a each of which corresponds to the bore 68in the first embodiment (a pair of bores not shown). The bores 68a extend through the body 61 of the plunger 60 and are therefore longer than the magnets 75 and 76, to enable adjustment of the longitudinal position of the magnets 75 and 76. In such case, the reed switching elements 50 and 55 may be identical and have contacts 53 and 58 disposed in the middle. The magnets 75and 76 would be moved to a selected location" to achieve the operation previously described of closing one pair of contacts before the other pair of contacts is closed.

. While there have been described what are at present considered. to be the preferred embodiments of theinve'ntion, it will be understood that various modifications may be made'therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, a pair of laterally spacedapart magnets operatively engaged by said plunger to be movable therewith between first and second limits along paths parallelto said predetermined path, a pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substannets toward said second limit, said contacts thereafter 7 being switched to the other condition thereof in response to movement of said magnets toward said first limit.

2. The reed switch set forth in claim l,wherein said housing is generally rectangular intransverse cross section.

3. The reed switch set forth in claim 1, wherein each of said magnets is permanently magnetized.

4. The reed switch set forth in claim I, wherein each of said magnets is a cylinder'having a length on the order of one-fourth inch and a diameter on the order of one-eighth inch. 7

5. The reed switch set forth in claim 1', wherein both of said magnets are mounted on and carried by said plunger.

6. The reed switch set forth in claim 1', wherein each of said magnets is a cylinder having an axis parallel to said predetermined path.

'7. The reed switch set forth in claim 1, wherein said contacts are disposed in a hermetically sealed'glass' envelope.

8. The reed switch set forth in claim 1, wherein said contacts are midway between said magnet paths.

9. The reed switch set forth in claim 1, wherein the distance between'said first and second limits is on the order of 0. 187 inches.

10. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, a pair of laterally spaced-apart magnets mounted on said plunger to be movable therewith between first and second limits along paths parallel to said predetermined path, spring biasing means operatively engaging said plunger and resiliently urging said magnets to said first limit, a pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets against said spring biasing means toward said'second limit, said contacts thereafter being switched to the other condition thereof in response to release of said plunger to cause said magnets to return toward said first limit.

11. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predeterminedpath, said plunger havinga pair of laterally spaced apart and longitudinallyextending bores therein and a channel laterally be,- tween said bores, a pair of magnets respectively in said bores of said plunger to be movable between first and second limits along paths parallel to said predetermined path, a pair of magnetically-responsive contacts in said housing and aligned with saidchannel and substantially parallel to said magnet paths and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets toward said second limit, said contacts thereafter being switched to the other condition thereof in response to movement of said magnets toward said first limit.

12. The reed switch set forth in claim 1 1, wherein the length of each of said bores is greater than the length of each of said magnets, whereby said magnets may be selectively located in said bores at a desired longitudinal position.

13. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, a first pair of laterally spaced-apart magnets operatively engaged by said plunger to be movable therewith between first and second limits along paths parallel to said predetermined path, a first pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said first pair of contacts being switched to one of the conditions thereof in response to movement of said first pair of magnets toward said second limit, said first pair of contacts thereafter being switched to the other condition thereof in response to movement of said first pair of magnets toward said first limit, a second pair of laterally-spaced apart magnets operatively engaged by said plunger to be movable therewith between first and second limits along paths parallel to said predetermined path, a second pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said second pair of contacts being switched to one of the conditions thereof in response to movement of said second pair of magnets toward said second limit, said second pair of contacts thereafter being switched to the other condition thereof in response to movement of said second pair of magnets toward said first limit.

14. The reed switch set forth in claim 13, wherein said first and second pairs of contacts are longitudinally spaced from each other.

15. The reed switch set forth in claim 13, wherein one of said pairs of contacts is normally open and the other of said pair of contacts is normally closed.

16. The reed switch set forth in claim 14, wherein said magnets are in the same longitudinal position relative to one another.

17. The reed switch set forth in claim 13, wherein each of said magnets is mounted on and carried by said plunger.

18. The reed switch set forth in claim 13, wherein said magnets are cylinders having longitudinal axes parallel to one another and said predetermined path.

19. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having a pair of laterally-spaced-apart and longitudinallyextending bores therein and a channel laterally between said bores, a pair of magnets respectively in said bores to be movable with said plunger between first and second limits along paths parallel to said predetermined path, a pair of magnetically-responsive contacts in said housing and aligned with said channel and substantially parallel thereto and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets toward said second limit, said contacts thereafter being switched to the other condition thereof in response to movement of said magnets toward said first limit.

20. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having first and second pairs of laterally-spaced-apart and longitudinally-extending magnet-receiving bores, said plunger having a longitudinally-extending first channel disposed laterally between said first pair of magnetreceiving bores and a longitudinally-extending second channel laterally between said second pair of magnetreceiving bores, a first pair of magnets respectively in said first pair of magnet-receiving bores to be movable with said plunger between first and second limits along paths parallel to said predetermined path, a first pair of magnetically-responsive contacts in said housing and aligned with said first channel and substantially parallel to the paths of said first pair of magnets and having open and closed conditions, said first pair of contacts being switched to one of the conditions thereof in response to movement of said first pair of magnets toward said second limit, said first pair of contacts thereafter being switched to the other condition thereof in response to movement of said first pair of magnets toward said first limit, a second pair of magnets respectively in said second pair of magnet-receiving bores to be movable with said plunger between said first and second limits along paths parallel to said predetermined path, a second pair of magnetically-responsive contacts in said housing and substantially parallel to the paths of said second pair of magnets and aligned with said second channel and having open and closed conditions, said second pair of contacts being switched to one of the conditions thereof in response to movement of said second pair of magnets toward said second limit, said second pair of contacts thereafter being switched to the other condition thereof in response to movement of said second pair of magnets toward said first limit.

21. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having a longitudinally extending central bore and first and second pairs of laterally-spaced-apart and longitudinally-extending magnet-receiving bores, saidplunger having a longitudinally-extending first channel disposed laterally between said first pair of magnet-receiving bores and a longitudinally-extending second channel laterally between said second pair of magnet-receiving bores, a first pair of magnets respectively in said first pair of magnet-receiving bores to be movable with said plunger between first and second limits along paths parallel to said predetermined path, a first pair of magnetically-responsive contacts in said housing and aligned with said first channel and substantially parallel to the paths of said first pair of magnets and having open and closed conditions, said first pair of contacts being switched to one of the conditions thereof in response to movement of said first pair of magnets toward said second limit, said first pair of contacts thereafter being switched to the other condition thereof in response to movement of said first pair of magnets toward said first limit, a second pair of magnets respectively in said second pair of magnet-receiving bores to be movable with said plunger between saidfirst and second limits along paths parallel to said predetermined path, a second pair of magnetically-responsive contacts in said housing and aligned with said second channel and substantially parallel to the paths of said second pair of magnets'and having open and closed conditions, said second pair of contacts being switched to one of the conditions thereof in response to movement of said second pair of magnets toward said second limit, said second pair of contacts thereafter being switched to the other condition thereof in response to movement of said second pair of magnets toward said first limit, and a socket in said housing for a lamp and aligned with said central bore.

i III l 

1. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, a pair of laterally spaced-apart magnets operatively engaged by said plunger to be movable therewith between first and second limits along paths parallel to said predetermined path, a pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets toward said second limit, said contacts thereafter being switched to the other condition thereof in response to movement of said magnets toward said first limit.
 2. The reed switch set forth in claim 1, wherein said housing is generally rectangular in transverse cross section.
 3. The reed switch set forth in claim 1, wherein each of said magnets is permanently magnetized.
 4. The reed switch set forth in claim 1, wherein each of said magnets is a cylinder having a length on the order of one-fourth inch and a diameter on the order of one-eighth inch.
 5. The reed switch set forth in claim 1, wherein both of said magnets are mounted on and carried by said plunger.
 6. The reed switch set forth in claim 1, wherein each of said magnets is a cylinder having an axis parallel to said predetermined path.
 7. The reed switch set forth in claim 1, wherein said contacts are disposed in a hermetically sealed glass envelope.
 8. The reed switch set forth in claim 1, wherein said contacts are midway between said magnet paths.
 9. The reed switch set forth in claim 1, wherein the distance between said first and second limits is on the order of 0.187 inches.
 10. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, a pair of laterally spaced-apart magnets mounted on said plunger to be movable therewith between first and Second limits along paths parallel to said predetermined path, spring biasing means operatively engaging said plunger and resiliently urging said magnets to said first limit, a pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets against said spring biasing means toward said second limit, said contacts thereafter being switched to the other condition thereof in response to release of said plunger to cause said magnets to return toward said first limit.
 11. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having a pair of laterally spaced apart and longitudinally-extending bores therein and a channel laterally between said bores, a pair of magnets respectively in said bores of said plunger to be movable between first and second limits along paths parallel to said predetermined path, a pair of magnetically-responsive contacts in said housing and aligned with said channel and substantially parallel to said magnet paths and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets toward said second limit, said contacts thereafter being switched to the other condition thereof in response to movement of said magnets toward said first limit.
 12. The reed switch set forth in claim 11, wherein the length of each of said bores is greater than the length of each of said magnets, whereby said magnets may be selectively located in said bores at a desired longitudinal position.
 13. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, a first pair of laterally spaced-apart magnets operatively engaged by said plunger to be movable therewith between first and second limits along paths parallel to said predetermined path, a first pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said first pair of contacts being switched to one of the conditions thereof in response to movement of said first pair of magnets toward said second limit, said first pair of contacts thereafter being switched to the other condition thereof in response to movement of said first pair of magnets toward said first limit, a second pair of laterally-spaced apart magnets operatively engaged by said plunger to be movable therewith between first and second limits along paths parallel to said predetermined path, a second pair of magnetically-responsive contacts in said housing disposed laterally between said magnet paths and substantially parallel thereto and having open and closed conditions, said second pair of contacts being switched to one of the conditions thereof in response to movement of said second pair of magnets toward said second limit, said second pair of contacts thereafter being switched to the other condition thereof in response to movement of said second pair of magnets toward said first limit.
 14. The reed switch set forth in claim 13, wherein said first and second pairs of contacts are longitudinally spaced from each other.
 15. The reed switch set forth in claim 13, wherein one of said pairs of contacts is normally open and the other of said pair of contacts is normally closed.
 16. The reed switch set forth in claim 14, wherein said magnets are in the same longitudinal position relative to one another.
 17. The reed switch set forth in claim 13, wherein each of said magnets is mounted on and carried by said plunger.
 18. The reed switch set forth in claim 13, wherein said magnets are cylinders having longitudinal axes parallel to one another and said predetermined path.
 19. A reEd switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having a pair of laterally-spaced-apart and longitudinally-extending bores therein and a channel laterally between said bores, a pair of magnets respectively in said bores to be movable with said plunger between first and second limits along paths parallel to said predetermined path, a pair of magnetically-responsive contacts in said housing and aligned with said channel and substantially parallel thereto and having open and closed conditions, said contacts being switched to one of the conditions thereof in response to movement of said magnets toward said second limit, said contacts thereafter being switched to the other condition thereof in response to movement of said magnets toward said first limit.
 20. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having first and second pairs of laterally-spaced-apart and longitudinally-extending magnet-receiving bores, said plunger having a longitudinally-extending first channel disposed laterally between said first pair of magnet-receiving bores and a longitudinally-extending second channel laterally between said second pair of magnet-receiving bores, a first pair of magnets respectively in said first pair of magnet-receiving bores to be movable with said plunger between first and second limits along paths parallel to said predetermined path, a first pair of magnetically-responsive contacts in said housing and aligned with said first channel and substantially parallel to the paths of said first pair of magnets and having open and closed conditions, said first pair of contacts being switched to one of the conditions thereof in response to movement of said first pair of magnets toward said second limit, said first pair of contacts thereafter being switched to the other condition thereof in response to movement of said first pair of magnets toward said first limit, a second pair of magnets respectively in said second pair of magnet-receiving bores to be movable with said plunger between said first and second limits along paths parallel to said predetermined path, a second pair of magnetically-responsive contacts in said housing and substantially parallel to the paths of said second pair of magnets and aligned with said second channel and having open and closed conditions, said second pair of contacts being switched to one of the conditions thereof in response to movement of said second pair of magnets toward said second limit, said second pair of contacts thereafter being switched to the other condition thereof in response to movement of said second pair of magnets toward said first limit.
 21. A reed switch comprising a housing, a plunger slidably carried by said housing and longitudinally movable along a predetermined path, said plunger having a longitudinally extending central bore and first and second pairs of laterally-spaced-apart and longitudinally-extending magnet-receiving bores, said plunger having a longitudinally-extending first channel disposed laterally between said first pair of magnet-receiving bores and a longitudinally-extending second channel laterally between said second pair of magnet-receiving bores, a first pair of magnets respectively in said first pair of magnet-receiving bores to be movable with said plunger between first and second limits along paths parallel to said predetermined path, a first pair of magnetically-responsive contacts in said housing and aligned with said first channel and substantially parallel to the paths of said first pair of magnets and having open and closed conditions, said first pair of contacts being switched to one of the conditions thereof in response to movement of said first pair of magnets toward said second limit, said first pair of contacts thereafter being switched to the other condition thereof in response to movement of said first pair of magnets toward said first limit, a second pair of magnets respectively in said second pair of magnet-receiving bores to be movable with said plunger between said first and second limits along paths parallel to said predetermined path, a second pair of magnetically-responsive contacts in said housing and aligned with said second channel and substantially parallel to the paths of said second pair of magnets and having open and closed conditions, said second pair of contacts being switched to one of the conditions thereof in response to movement of said second pair of magnets toward said second limit, said second pair of contacts thereafter being switched to the other condition thereof in response to movement of said second pair of magnets toward said first limit, and a socket in said housing for a lamp and aligned with said central bore. 